The long term goal of this project to understand how the functions of type II myosin are regulated. The entire superfamily of cytoskeletal myosins have been classified based on sequence similarities among their motor domains (Cheney et al.,, 1993). Five cytoskeletal myosins have been identified in Saccharomyces cerevisiae. with three representative classes to date. Although an essential role in post-Golgi vesicle transport has been demonstrated for a yeast type V myosin, Myo2p (Johnston et al., 1991, Govindan et al., 1995), the functions of other yeast myosins such as the type I myosins, Myo3p and Myo5p (Goodson et al., 1994), and a second type V myosin, Myo4p (Lillie and Brown, 1994) are not clear. The yeast type II myosin, Myo1p appears to be important for cytokinesis (Watts et al., 1987). There is evidence for redundancy among myosin functions which may explain th non-lethality of most myosin gene knockout mutations. A recently identified kinesin-like motor protein, Smy1p, has been shown to be functionally redundant with both myosins Myo1p and My02p which suggests that other classes of motor proteins with similar functions exist (Brown pers. comm., and Lillie and Brown, 1994 respectively). To achieve our long term goal, it is necessary to identify gene products redundant with Myo1p. Identification of these genes will allow the development appropriate deletion strains in which to express and apply functional tests in vivo for mutated recombinant MY01 genes. These studies will also expand our understanding of the type of interactions between type II myosins and other cellular proteins. The specific aims of this proposal are: 1) To carry out a genetic screen to identify synthetic lethal mutations (sl's) of myo1 in order to identify, characterize and mutate the genes encoding protein which are functionally redundant with Myo1p. 2) As a long term extension of aim #1, multi-copy suppressors of the my01 synthetic lethal phenotype (my01,sl) will be sought to identify gene products that can rescue the synthetic lethal phenotypes. This approach has been used successfully for another motor protein gene by lillie and Brown (1994). 3) We will explore the possible correlation between Myo1p and normal cellular localization and function of chitinase (Cts1p) to test whether the delay in cytokinesis observed in my01 mutants reflects a role for Myo1p in the intracellular transport of components required for cell wall metabolism during cell division. 4) To train students in research leading to graduate degrees in the biomedical sciences.